Xpert CARBA-R Assay for the Detection of Carbapenemase-Producing Organisms in Intensive Care Unit Patients of a Korean Tertiary Care Hospital

Carbapenemase-producing organisms (CPO) are rapidly disseminating worldwide, and their presence in tertiary care hospitals poses a significant threat to the management of nosocomial infections. There is a need to control CPO, especially in intensive care unit (ICU) patients, because these organisms are resistant to most beta-lactam antibiotics and are easily transmitted. At present, the identification of CPO is time-consuming; hence, this study focused on the use of the Xpert CARBA-R assay (Cepheid, USA) to determine intestinal colonization rates of CPO in patients admitted to the ICU of a tertiary care hospital in Korea. Forty clinical stool samples were collected and inoculated both in a CARBA-R cartridge and in conventional culture plates. The CARBA-R assay required only ~one hour to screen CPO, while the time required for conventional culture was over three days. We also found that the prevalences of intestinal colonization by carbapenem-resistant organisms and Enterobacteriaceae were 17.5% (7 out of 40) and 7.5% (3 out of 40), respectively. Among the colonizing strains, three that contained carbapenemase, including Klebsiella pneumonia carbapenemase (KPC), and imipenem (IMP) and Verona integron-mediated metallo-beta-lactamase (VIM) were found. With its convenience, the Xpert CARBA-R assay can be included in CPO surveillance strategies.

Establishing Quality Control Ranges for Antimicrobial Susceptibility Testing of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus: A Cornerstone to Develop Reference Strains for Korean Clinical Microbiology Laboratories

Quality control (QC) processes are being performed in the majority of clinical microbiology laboratories to ensure the performance of microbial identification and antimicrobial susceptibility testing by using ATCC strains. To obtain these ATCC strains, some inconveniences are encountered concerning the purchase cost of the strains and the shipping time required. This study was focused on constructing a database of reference strains for QC processes using domestic bacterial strains, concentrating primarily on antimicrobial susceptibility testing. Three strains (Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus) that showed legible results in preliminary testing were selected. The minimal inhibitory concentrations (MICs) and zone diameters (ZDs) of eight antimicrobials for each strain were determined according to the CLSI M23. All resulting MIC and ZD ranges included at least 95% of the data. The ZD QC ranges obtained by using the CLSI method were less than 12 mm, and the MIC QC ranges extended no more than five dilutions. This study is a preliminary attempt to construct a bank of Korean QC strains. With further studies, a positive outcome toward cost and time reduction can be anticipated.